Process for the production of superconductive wires and bands



United States Patent 6 3 Claims. of. 148-115) The present invention relates to an improved process for the production of superconductive wires and bands and more particularly to the production of such superconductive wires and bands from titanium niobium alloys.

It is known that wires and bands of so-called hard superconductors, that is, such superconductors the maximum current density of which in the range of superconductivity is only little influenced by exterior magnetic fields even up to high field strengths, can be produced by cold working of niobium zirconium alloys. Such alloys, however, have the disadvantage that they are difiicult to process to wires and bands.

According to the invention it was found that titaniumniobium alloys with 20-45% by weight of niobium, which per se are already known as superconductor alloys can be processed to superconductive wires and bands in an especially advantageous manner. In the process according to the invention, the starting alloys consisting of 20- 45% by weight of niobium and the remainder titanium are first cooled down from the ,8 region, that is, from a temperature above 700 C., preferably above 900 C., so rapidly that the 5 phase is retained along with the mar tensite (supersaturated a mixed crystals) which is formed but that no equilibrium or phase occurs. The quenching medium required to eifect such cooling depends upon the thickness of the alloy workpiece and with thin workpieces can be air whereas with thicker workpieces water may be required. The required rapid cooling for retention of the B phase can also be effected in the casting, for example, by casting a bar mm. thick ina water cooled copper mold under argon. Castings or hot worked bars or rods which are easily produced can be used as the starting materials for the production of the thus rapidly cooled alloys which are then cold worked to wires or hands to provide a degree of deformation of 60 to 99%, preferably between 90-99%, and these then given a heat treatment between 250 and 650 C. In the production of the wires and bands from the rapidly cooled starting material which primarily exhibits the B phase, a martensitic lamellar structure is developed. During the subsequent heat treatment the supersaturated ,8 and martensitic phase separate out whereby intermediate phases of lamellar like structure are formed which exhibit very excellent superconductive properties. As a result the heat treatment following the cold working must be carried out in the 1x 8 range and also should be shorter at the higher temperatures than at the lower temperatures within the range indicated. The duration of the heat treatment and the temperature thereof must be adjusted with respect to each other in each individual case in such a way that the supersaturated or and 5 mixed crystals disintegrate and can, for example, last for 100 hours. The proper adjustment can be easily determined by simple preliminary tests by ascertaining what combination gives the best results. In any event, the heat treatment must be carried out in such a way that the lamellar structure produced by the cold working is retained and that as little as possible, if any, coarse grained or titanium is formed.

Very unexpected-1y it was found that wires and bands according to the invention exhibit high critical current 3,271,200 Patented Sept. 6, 1966 densities at 5 K., namely, over 100,000 A./cm. without having the superconductivity impaired.

Preferably, alloys are employed according to the inven tion which are composed of 30% to 40% by weight of niobium and the remainder titanium. Also, preferably, the heat treatment carried out on the wires and bands produced therefrom is for 10-25 hours at temperatures between 350 and 600 C.

The heat treatment need not necessarily be carried out only after all of the cold working has been completed as it is possible to follow the heat treatment by a slight cold working which may provide a degree of deformation of up to The following example will serve to illustrate the process according to the invention:

Example A casting of an alloy of the stoichiometric composition NbTi that is, 33% by weight of niobium, the remainder titanium, was hot and cold rolled to a rod 2 mm. in diameter heated to 900 C. so as to be in the ,3 range and quenched in water so rapidly that no equilibrium on phase was produced. Subsequently the rod was cold drawn to a wire 0.2 mm. in diameter. One portion of the wire was annealed for 24 hours at 375 C. and another for 24 hours at 590 C.

The resulting wire stock had the following superconductive properties at 5 K.

I claim:

1. Method of producing superconductive wires and bands from titanium-niobium alloys composed of 20-45% by weight o-f niobium and the remainder titanium which comprises cooling down such an alloy from a temperature in the 5 phase region sufficiently rapidly that such [3 phase is retained and in addition a martensitic phase but no equilibrium or phase is produced, cold working such cooled alloy to wires and bands and subjecting such cold worked wires or bands to a heat treatment between 250 and 650 C. to cause the supersaturated B and martensitic phases therein to separate out.

2. The process of claim 1 in which said cold working provides a degree of deformation between about 60 and 99%.

3. The process of claim 1 in which said cold working provides a degree of deformation between 60 and 99% and said subsequent heat treatment is from 10-25 hours at a temperature between 350 and 600 C.

References Cited by the Examiner High-Field Superconducting Characteristics of Some Duchle Transition Metal Alloys, Hake et al., Superconductors, AIM'E, February 1962, pages 53-58.

Superconducting Solid Solution Alloys of the Transition Elements, Hulm et al., Physical Review, vol. 123, No.5, p. 1574-1576.

HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, H. F. SAITO, Assistant Examiners. 

1. METHOD OF PRODUCING SUPERCONDUCTIVE WIRES AND BANDS FROM TITANIUM-NIOBIUM ALLOYS COMPOSED OF 2:-45% BY WEIGHT OF NIOBIUM AND THE REMAINDER TITANIUM WHICH COMPRISES COOLING DOWN SUCH AN ALLOY FFROM A TEMPERATURE IN THE B PHASE REGION SUFFICIENTLY RAPIDLY THAT SUCH B PHASE IS RETAINED AND IN ADDITION A MATENSITIC PHASE BUT NO EQUILIBRIUM A PHASE IS PRODUCED, COLD WORKING SUCH COOLED ALLOY TO WIRES AND BANDS AND SUBJECTING SUCH COLD WORKED WIRES OR BANDS TO A HEAT TREATMENT BETWEEN 250 AND 650* C. TO CAUSE THE SUPERSATURATED B AND MARTENSITIC PHASES THEREIN TO SEPARATE OUT. 